Dear sir,

I have some inquiries about the choice of noun form (singular or plural) to be used with a plural possessive determiners (their, our, etc.) I have sought the advice of some native speakers on the following 4 sentences only to become more confused as they have different opinions. It is really really frustrating.

1a. There are many cells in *our ***.
1b. There are many cells in *our ***.

2a. We do this in *our everyday ***.
2b. We do this in *our everyday ***.

A Canadian native speaker and a reply from ASKOXFORD advised that only (1b) and (2b) are correct.
An American professor of English advised that I should use (1a) and (2a) to 'avoid the problem of thinking that we have more than one body apiece' and likewise with 'life'.
A reply from Englishclub.com advised that all four are acceptable.

Whose opinion is correct or more reliable? The professor's?
Is there such a thing as 'the ultimate authority' in English from which/whom I can seek advice? Please help.

I have seen the use of plural possessive determiners with singular noun in some books and on the Net. So does that make such use acceptable?

In Longman Dictionary of Common Errors (Turton & Heaton, 1996), there is this sentence:
1. This example shows how computers affect *our everyday ***. (pg 122)

In Collins Cobuild English Dictionary for Advanced Learners (3rd ed, 2001):
1. All of us in *our daily *** react favourably to people who take us and our
views seriously. (pg 377)

2. ...*our body'*** sensory system (pg 1411)

3. People also use 'heart' to refer to the area of *their *** that is closest
to *their ***. (pg 725)

In Biology; The Unity and Diversity of Life (10th ed., Starr & Taggart, 2003, Thomson Brooks/Cole):
1. Tuataras are like modern amphibians in some respects of *their *** and in their way of walking. (pg 457).
2. Chameleons rely on *their ***, which is longer than *their ***. (pg 456)

On the Net, at the website of SocietyGuardian.co.uk:
1. People wait for years,decades, in pain, in the faint hope that one day they will receive the call from the hospital that will return *their *** to normal.

2. It assumes that change is difficult without reference to the subject's family, school, and - for priests - transition to the seminary, their experiences there and *their *** as *a ***.

Michael Swan's Practical English Usage says that for generalisations and rules, it is OK to use singular or plural nouns or both together with 'their/our'. So, is it applicable here?

Thank you.
I think all forms are acceptable, Ryan.
In my opinion, the American professor is right that the 1st sentence
"We have many cells in our body" avoids a problem of thinking there could be more than one body, admittedly it is obvious, that there is only one body, one heart, etc. for one person.
This sentence refers rather to any human being as an individual while
"We have many cells in our bodies" would refer to all human beings as a whole.
But this is only a very slight difference and therefore none of your examples would be wrong (you can see that it is used either way in all the other examples you found and mentioned) - even I'd agree to the professor and prefer the 1st example.
Would then the following be correct?

You are a camaleon or You are camaleons.

There are some people who have ice cubes in their hearts filled with whiskies.

I would agree with n2.

You shouldn't make our hearts suffer.
They shouldn't make their hearts suffer. Their is applicable here.

They are both likely to occurr as they are generalisations.
Students: We have free audio pronunciation exercises.
I think we could say " You have no blood in your veins", couldn't we?
 Pemmican's reply was promoted to an answer.
Thanks guys.

I sought help from usingenglish.com too. The teacher there said that there only the second sentences are correct. He said the professor was 'perhaps, the original nutty professor' and the englishclub.com person didn't understand my question.

But unluckily he didn't answer all my question, eg. is there such thing as 'the ultimate authority' in English?

If he is right, then Collins Cobuild English Dictionary for Advanced Learners and Longman Dictionary of Common Errors and the Biology textbook published by Thomson/Brooks-Cole are all using poor English?

Personally I trust the editorial capability of these publishers!
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This doesn't help!